The NIST-F1 atomic clock that currently serves as primary time and frequency standard for the U.S. is expected to neither gain nor lose a second in more than 100 million years. That might sound pretty accurate, but a proposed nuclear clock could make it look like a cheap digital wristwatch. It is claimed that the proposed clock would neither gain nor lose 1/20th of a second in 14 billion years. To put that in context, that’s the estimated age of the universe.